1. Field of the Invention
The present invention relates to a display driver for driving a display section and a display device using the display driver.
2. Description of Related Art
In a display device which includes a liquid crystal panel (a display panel in a broader sense) having a large display capacity such as a LCD for vehicle mounting, a LCD for a copying machine or the like, the display driving is performed using a plurality of display drivers (liquid crystal driving circuits) In general, these display drivers are constituted such that they are classified into the master side and the slave side. In this case, conventionally, a liquid crystal driving power source circuit is arranged only at the master-side display driver and a liquid crystal driving power source circuit is not arranged at the slave-side display drivers.
FIG. 8 schematically shows the constitution of the conventional display device which includes the master-side display driver and the slave-side display drivers.
At the master-side display drivers a resistor 10 is inserted between a power source voltage VDD at the high potential side and a power source voltage VSS at the lower potential side. Potentials V1, V2 which are divided by the resistor 10 are inputted into operational amplifiers 21, 22 to which negative feedback loops are formed. Voltages V11, V12 which are substantially equal to the input potentials are outputted from these operational amplifiers.
At the master side, the voltage V11 which is outputted from the operational amplifier 21 is supplied to a series of driver cells 31, 32, 33, . . . for driving liquid crystal as a power source. Further, the voltage V12 which is outputted from the operational amplifier 22 is supplied to a series of driver cells 31, 32, 33, . . . for driving liquid crystal as a power source.
The voltages V11, V12 which are outputted from the master-side operational amplifiers 21, 22 are also supplied to the slave side as voltages V11′, V12′ through interconnecting lines 51, 52 formed on an interconnect layer on a glass substrate. At the slave side, the voltage V11′ is supplied to a series of driver cells 71, 72, 73, . . . for driving liquid crystal as a power source. Further, the voltage V12′ is supplied to a series of driver cells 71, 72, 73, . . . for driving liquid crystal as a power source.
However, recently, there has been a tendency that the area of a liquid crystal panel is enlarged so as to increase a capacity of the liquid crystal panel. Accordingly, the electric power capacity which is required at the slave side is also increased. Further, in a chip-on-glass (Chip On Glass: abbreviated as COG hereinafter) structure which forms integrated display drivers on a glass substrate, the thickness of an interconnect layer is thin and hence, the resistance of the interconnecting line which connects the master side and the slave side is increased. Accordingly, a voltage drop occurs between the master-side power source voltages V11, V12 and the slave-side power source voltages V11′, V12′.
In FIG. 9, schematic waveforms of the master-side power source voltages V11, V12 and of the slave-side power source voltages V11′, V12′ are shown.
In this manner, since the parasitic resistance is inserted to the interconnecting line which connects the master side and the slave side, the capacity of the driver output becomes different between the master side and the slave side. To be more specific, compared to the output waveform of the master-side power source voltages V11, V12, the output waveform of the slave-side power source voltages V11′, V12′ loses sharpness. As a result, there arises problems such as giving rise to the deviation in bias on the whole screen and the display quality becoming different between the master side and the slave side due to the occurrence of the block irregularities at a portion of the screen.